As the generation of devices advances, the goal of a higher performance trend cannot be achieved only by a scaling effect with a conventional bulk silicon wafer, and a new device structure is accordingly needed. An SOI wafer has been paid attention to as a starting raw material. Furthermore, since the types of devices using the SOI wafer increase, thicknesses of buried oxide films in addition to SOI layers are demanded in a wide range.
As a typical manufacturing method of this SOI wafer, there are known, for example, a bonding method or a SIMOX method in which high concentration oxygen ions are implanted into a silicon wafer and thereafter a heat treatment is performed at a high temperature to form an oxide film inside the wafer. The bonding method is a method for manufacturing the SOI wafer having the SOI layer formed on a buried oxide film as an insulator by means of: forming an oxide film on at least one of a bond wafer on which the SOI layer is to be formed and a base wafer that is to be a supporting substrate; bonding the bond wafer to the base wafer through the oxide film; and thinning the thickness of the bond wafer.
From the viewpoint of being capable of manufacturing the SOI layer with a uniform thickness in a wide thickness range in case of the fabrication of a thin SOI layer, the SOI wafer has been mainly used which is manufactured by using an ion implantation delamination method (also called as the Smart Cut method (registered trademark)), which is one of the bonding method, among these manufacturing methods of the SOI wafer using the bonding method.
In the ion implantation delamination method, the buried oxide film is generally formed by growing an oxide film on the wafer prior to the bonding. The thickness of the buried oxide film of the SOI wafer can be controlled by controlling the thickness of the oxide film during the oxide film growth prior to the bonding. The control range can be wide. In case of a thin thickness of the buried oxide film, however, it is apt to become difficult to bond the wafers. Therefore, there arise problems that it is easy to generate defects called voids or blisters to the SOI wafer, and further the wafers are not bonded so that the SOI layer is not formed.
For the purpose of adjustments of the thickness of the SOI layer and a surface state thereof, various heat treatments may be performed after forming the SOI layer by delamination at an ion implanted layer. In this case, it is known that the thickness of the buried oxide film in addition to the thickness of the SOI layer at the surface change, and it is necessary to control the thickness of the buried oxide film also during heat treatment processes in the manufacture of the SOI wafer. This means that the thickness of the buried oxide film can be actively adjusted by the control during the heat treatment processes in the manufacture of the SOI wafer.
The methods in Patent Literature 1 and Patent Literature 2 are known as an adjustment method of the thickness of the buried oxide film by a heat treatment for reducing the thickness of the buried oxide film in the manufacture of the SOI wafer.
As described in Patent Literature 1 and Patent Literature 2, a method for manufacturing a SOI wafer having few defects was developed in which the wafers are bonded in such a manner that the thickness of the buried oxide film is thicker than a final target thickness, and thereafter the thickness is reduced during a heat treatment process in the manufacture of the SOI wafer. In this method, however, in-plane uniformity for a decrease in the thickness of the buried oxide film deteriorates due to nonuniformity of a gas used in the heat treatment, a heat treatment temperature, or the like. As a result, there arises a problem that in-plane distribution of the buried oxide film consequently deteriorates.
Citation List
Patent Literature
    Patent Literature 1:Japanese Unexamined Patent publication (Kokai) No.2004-221198    Patent Literature 2:Japanese Unexamined Patent publication (Kokai) No.2006-156770